The present invention relates to an operating procedure for the motor of an electric powered tool such as a hammer drill, the operating idle time of which is set to a value using control electronics, which is the same as or slightly higher than the chosen operating speed. The invention also relates to an electric powered tool with specific features to realise the operating procedure.
The durability and operational readiness of the motor of an electric powered tool depends on the motor temperature. Too high a temperature can result in the motor not being able to be run for a certain time while cooling down. Thus, the temperature of the motor should not exceed a certain temperature during operation. The higher the moment of strain that has to be applied to the motor, the more the motor temperature continues to increase. The temperature falls when the motor is run on idle time. The cooling system is improved due to the increased air flow at high engine speeds.
The operating speed is the engine speed of the motor under strain: it is determined by the operating process or specific operating conditions. The engine speed drops when the motor has to be run on an extremely high moment of strain due to the natural characteristic line for strain in the motor (see FIG. 3).
The operating idle speed for the comfortable operation of the electric powered tool should not be much higher than operating speed when the motor is no longer strained, i.e. it is running on idle speed. This would be annoying in hammer drills when the tool is switched off and then switched on again. There should be no major variations in the operating idle speed, as they can also have an interfering effect. The operating idle speed of the motor is thus always limited to a favourable level only slightly above the chosen operating speed.
U.S. Pat. No. 4,307,325 proposes that a strain index be determined according to the amount of time in which a motor is run on idle speed and under strain—with which the temperature of the motor can be determined with only slight complexity. The motor is switched off to prevent damage done should the temperature exceed a certain value. The electric powered tool can only be switched on again when the motor is cooled down, i.e. the electric powered tool cannot be used for a certain amount of time.
The complete switch off of the motor results in an interruption in the cool airflow so that cooling only takes places slowly. DE 30 21 689 AI suggests that the motor be switched off, but that the input is limited in an overload, maintaining a sufficiently high engine speed below the operating idle speed to cool the motor. This, however, does not only take place in the coil overheating. Additionally, the cooling effect is not optimal, as the engine speed of the motor is not sufficiently high due to the limited input. Motor failure due to overheating thus cannot be prevented in certain cases.